1. Field of the Invention
The present invention is broadly concerned with improved methods for the production fo highly desirable solid articles (e.g., sheets, panels, bricks, mold pourings) containing expanded perlite and cement. More particularly, the invention is concerned with such methods wherein expanded perlite is first treated by application of cement binder, followed by mixing of cement with the treated perlite to form a castable or formable mixture.
2. Description of the Prior Art
Perlite is a generic term for naturally occurring siliceous volcanic rock. A distinguishing feature of perlite is that when heated to a suitable point in its softening range, it expands four to twenty times its original volume. This expansion is due to the presence of 2-6% combined water in the crude perlite rock. When quickly heated above 1600° F., the crude rock pops in a manner similar to popcorn as the combined water vaporizes, creating countless tiny bubbles in the heat-softened glassy particles. It is the presence of these tiny glass-sealed bubbles which accounts for the desirable physical properties of expanded perlite. Expanded perlite can be manufactured to weigh from 2-15 lb/cubic foot, making it adaptable for numerous applications in the construction, industrial, chemical, horticultural and petrochemical industries.
Expanded perlite has been used in the past in the fabrication of lightweight building materials and artificial stones. Thus, U.S. Pat. No. 4,043,826 describes a process for making artificial rocks wherein latex paint, water, calcium chloride, Portland cement mid horticultural perlite are mixed together and poured into a flexible mold in the shape of a natural rock. U.S. Pat. No. 3,847,633 is directed to the production of building materials wherein Portland cement and perlite are mixed together along with plaster of paris, fly ash and fiberglass reinforcing material. In the process, dry materials are pre-blended, followed by the addition of water and mixing; the resulting slurry is then formed using a specific, two-stage, differential temperature curing regimen. U.S. Pat Nos. 2,858,227 and 4,042,046 describe additional variants of these processes for the production of perlite/cement products.